Active material for batteries, non-aqueous electrolyte battery, and battery pack

ABSTRACT

According to one embodiment, an active material for batteries includes monoclinic β-type titanium composite oxide containing at least one element selected from the group consisting of V, Nb, Ta, Al, Ga, and In, the at least one element being contained in an amount of 0.03 wt % or more and 3 wt % or less.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of PCT Application No.PCT/JP2009/059803, filed May 28, 2009, the entire contents of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a active material forbatteries, a non-aqueous electrolyte battery, and a battery pack.

BACKGROUND

Titanium oxide having a monoclinic β-type structure (hereinafterreferred to as TiO₂(B)) has recently been noted as an active materialfor a non-aqueous electrolyte battery (see JP-A 2008-34368 (KOKAI), JP-A2008-117625 (KOKAI) and WO 2009/028553 A1). The number of lithium ionswhich can be inserted and released per unit chemical formula of spineltype lithium titanate (Li₄Ti₅O₁₂) which has heretofore been put intopractical use is three. Therefore, the number of lithium ions which canbe inserted/released per titanium ion is 3/5, i.e., the theoreticalmaximum number is 0.6. In contrast, in TiO₂(B), the maximum number oflithium ions which can be inserted/released per titanium ion is 1.0.Therefore, TiO₂(B) has a theoretical capacity of about 335 mAh/g whichis an excellent property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a flat non-aqueous electrolytebattery according to one embodiment;

FIG. 2 is an enlarged sectional view showing a part A of FIG. 1;

FIG. 3 is an exploded perspective view showing a battery pack accordingto the embodiment;

FIG. 4 is a block diagram showing the battery pack of FIG. 3;

FIG. 5 is a diagram showing an X-ray diffraction pattern of titaniumcomposite oxide of Example 1; and

FIG. 6 is a diagram schematically showing a crystal structure ofmonoclinic β-type titanium oxide (TiO₂(B)).

DETAILED DESCRIPTION

Hereinafter, the active material for batteries, a non-aqueouselectrolyte battery, and battery pack according to the embodiments aredescribed below with reference to drawings.

In general, according to an embodiment, an active material for batteriescomprises monoclinic β-type titanium composite oxide containing at leastone element selected from the group consisting of V, Nb, Ta, Al, Ga, andIn, the at least one element being contained in an amount of 0.03 wt %or more and 3 wt % or less.

It is possible to measure the content of the at least one elementselected from the group consisting of V, Nb, Ta, Al, Ga, and In by ICPemission spectroscopy. The measurement of the content of the element bythe ICP emission spectroscopy is conducted by the following method, forexample. A battery is disassembled in a discharge state, and anelectrode (e.g., a negative electrode) is taken out, followed bydeactivation of a negative electrode layer in water. After that,titanium composite oxide in the negative electrode layer is extracted.The extraction treatment may be performed by eliminating a conductiveagent and a binder in the negative electrode layer by a heat treatmentin air, for example. After transferring the extracted titanium compositeoxide to a container while measuring the titanium composite oxide, acidfusion or alkali fusion is performed to obtain a measurement solution.ICP emission spectroscopy of the measurement solution is conducted byusing a measurement apparatus (e.g., SPS-1500V manufactured by SIINanotechnology Inc.) to measure a content of the element.

A structure of the monoclinic titanium dioxide is indicated as TiO₂(B).The crystal structure indicated as TiO₂(B) primarily belongs to thespace group C2/m and has a tunneling structure as shown in FIG. 6.Detailed crystal structure of TiO₂(B) can be found in the documents ofR. Marchang, L. Brohan, and M. Tournoux; Material Research.

As shown in FIG. 6, in the crystal structure indicated as TiO₂(B), atitanium ion 53 and oxide ions 52 form a skeletal structure part 51 a,and the skeletal structure parts 51 a are alternately disposed. Aclearance part 51 b is formed between the adjacent skeletal structureparts 51 a. The clearance part 51 b can be a host site for intercalation(insertion) of a foreign atom. It has been known that a host site whichis capable of insertion/release of a foreign atom exist on a crystalsurface of TiO₂(B). When lithium ions are inserted into or released fromthe host sites, TiO₂(B) inserts and releases the lithium ions in areversible manner.

When the lithium ion is inserted into the clearance part 51 b, Ti⁴⁺forming the skeleton is reduced to Ti³⁺, so that electrical neutralityof the crystal is maintained. Since TiO₂(B) has one Ti⁴⁺ per chemicalformula, it is possible to insert between layers one lithium ion at themaximum in theory. Therefore, a titanium oxide compound having theTiO₂(B) crystal structure is represented by a general formula Li_(x)TiO₂(0≦x≦1). In this case, it is possible to obtain a theoretical capacityof 335 mAh/g, which is almost twice of titanium dioxide described inJP-A 2008-34368 (KOKAI) and JP-A 2008-117625 (KOKAI).

However, since the above-described TiO₂(B) is an insulator, it isdifficult to fully exploit its high capacity. Further, high currentcharacteristics of a non-aqueous electrolyte battery containing suchTiO₂(B) as an active material are degraded.

In view of the above, the embodiment enables to improve an electronconduction property of TiO₂(B) by adding a predetermined amount of atleast one element selected from the group of V, Nb, Ta, Al, Ga, and Into the monoclinic β-type titanium oxide (TiO₂(B)). Therefore, it ispossible to fully exploit the high capacity property of TiO₂(B), therebymaking it possible to obtain a active material for batteries whichcontributes to high current characteristics and an excellentcharge-discharge cycle property when incorporated into a battery.

For the at least one element selected from the group consisting of V,Nb, Ta, Al, Ga, and In, Nb is preferred. It is preferable to use Nb andV or Nb and Ta in the case of using two or more species of the elementsor to use three species of Nb, V, and Ta of the elements.

When the content of the at least one element is less than 0.03 wt %, itis difficult to attain the improvement in electron conduction propertyand an effect of stabilizing crystal structure of TiO₂(B). On the otherhand, the content of the at least one element exceeds 3 wt %, adifferent phase appears in TiO₂(B), thereby raising a risk ofdeteriorating electric capacity and charge-discharge cycle property. Theat least one element is more preferably contained in an amount 0.03 to 1wt % in the sum of the titanium composite oxide and the at least oneelement.

TiO₂(B) contained the at least one element may preferably have a primaryparticle diameter of 100 nm or more and 1 μm or less. If the primaryparticle diameter is 100 nm or more, handling is facilitated in terms ofindustrial production. On the other hand, if the primary particlediameter is 1 μm or less, it is possible to smoothly diffuse lithiumions into a solid of TiO₂(B).

TiO₂(B) contained the at least one element may preferably have aspecific surface area of 5 m²/g or more and 50 m²/g or less. When thespecific surface area is 5 m²/g or more, it is possible to ensuresufficient insertion/desorption sites for lithium ions. On the otherhand, the specific surface area is 50 m²/g or less, handling isfacilitated in terms of industrial production.

Hereinafter, a production process for the active material for batteriesaccording to the embodiment will be described.

To start with, a starting material is prepared, which is obtainable byadding a predetermined amount of at least one element selected from thegroup consisting of V, Nb, Ta, Al, Ga, and In to an alkali titanatecompound such as Na₂Ti₃O₇, K₂Ti₄O₉, and Cs₂Ti₅O₁₂. It is possible tosynthesize potassium titanate (K₂Ti₄O₉) by a flux method, for example.It is possible to synthesize the alkali titanate compound containing theat least one element by mixing a material containing as a constituentelement the at least one element selected from the group consisting ofV, Nb, Ta, Al, Ga, and In, a material containing Ti, and a materialcontaining an alkali element such as Na, K, and Cs at predeterminedratios and by employing an ordinary solid phase reaction. A method and acrystal shape in the synthesis of the starting material are not limited.

The starting material is washed well with pure water to eliminateimpurities from the alkali titanate compound, and then an acid treatmentis performed to exchange alkali cations with protons. It is possible toperform the exchange with protons of sodium ions, potassium ions, andcesium ions contained in sodium titanate, potassium titanate, and cesiumtitanate without breaking the crystal structures. The proton exchange byacid treatment is performed by adding hydrochloric acid having aconcentration of 1M to the starting material, followed by stirring. Itis desirable to perform the acid treatment until the proton exchange issatisfactorily completed. A pH may be adjusted during the protonexchange by adding an alkalizing solution to the solution. After theproton exchange, washing with pure water is performed again.

Before performing the proton exchange, it is preferable to pulverize thestarting material by using a ball mill. The pulverization enables theproton exchange to be smoothly performed. As pulverization conditions, azirconia ball having a diameter of 10 to 15 mm is used per 100 cm² of acontainer, and the zirconia ball is rotated at a rotation speed of 600to 1000 rpm for about 1 to 3 hours. Pulverization for one hour or lessis not preferred since the starting material is not satisfactorilypulverized by such pulverization. Further, long-time pulverization of 3hours or more is not preferred since a mechanochemical reaction ispromoted by such pulverization to cause a phase separation into acompound different from the target product.

By washing and drying a product obtained after the completion of protonexchange, a proton exchange product which is an intermediate product isobtained. Subsequently, TiO₂(B) (final product) containing the at leastone element selected from the group consisting of V, Nb, Ta, Al, Ga, andIn is produced by subjecting the proton exchange product to a heattreatment.

A preferred heating temperature is from 250 to 500° C. When the heatingtemperature is less than 250° C., crystallinity is considerablydeteriorated to deteriorate electrode capacity, charge-dischargeefficiency, and repetition property. On the other hand, when the heatingtemperature exceeds 500° C., an impurity phase such as an anatase phaseis generated to raise a risk of a reduction of capacity. A morepreferred heating temperature is 300 to 400° C.

It is possible to use the active material for batteries according to theembodiment not only for a negative electrode which will be describedlater in this specification but also for a positive electrode, and highcurrent characteristics are attained in either use. More specifically,the high current characteristics are the effect attained by containingthe at least one element selected from the group consisting of V, Nb,Ta, Al, Ga, and In, and the effect attained in the use for the positiveelectrode is not different from that attained in the use for thenegative electrode. Therefore, it is possible to use the active materialfor batteries according to the embodiment for either of the negativeelectrode or the positive electrode and to attain the same effect.

In the case of using the active material for batteries according to theembodiment for the positive electrode, an active material of thenegative electrode as the counter electrode may be metal lithium, alithium alloy, or a carbon-based material such as graphite and coke.

Hereinafter, a non-aqueous electrolyte battery according to theembodiment will be described.

The non-aqueous electrolyte battery according to the embodiment includesa outer case; a positive electrode housed in the outer case; a negativeelectrode housed in the outer case so as to spatially separate by aseparator, for example, from the positive electrode and comprising anactive material; and a non-aqueous electrolyte contained in the outercase. The active material of the negative electrode comprises monoclinicβ-type titanium composite oxide containing at least one element selectedfrom the group consisting of V, Nb, Ta, Al, Ga, and In. The at least oneelement is contained in an amount of 0.03 wt % or more and 3 wt % orless.

Hereinafter, the outer case, negative electrode, positive electrode,separator, and non-aqueous electrolyte which are the constituent membersof the non-aqueous electrolyte battery will be described in detail.

1) Outer Case

The outer case is formed from a laminated film having a thickness of 0.5mm or less. Further, a metallic container having a thickness of 1.0 mmor less is used for the outer case. The metallic container may morepreferably have a thickness of 0.5 mm or less.

Examples of a shape of the outer case include a flat type (thin type), asquare type, a cylinder type, a coin type, a button type, and the like.Examples of the outer case include a outer case for a small batterywhich is mounted to a mobile electronic appliance and a outer case for alarge battery which is mounted to a two-wheel or four-wheel automobile.

As the laminated film, a multilayer film in which a metal layer isformed between resin layers is used. The metal layer may preferably bean aluminum foil or an aluminum alloy foil for attaining a light weight.As the resin layer, a polymer material such as polypropylene (PP),polyethylene (PE), nylon, polyethylene terephthalate (PET), and the likemay be used. The laminated film may be molded into the shape of theouter case by sealing by thermal fusion bonding.

The metallic container is made from aluminum, an aluminum alloy, or thelike. The aluminum alloy may preferably be an alloy containing anelement such as magnesium, zinc, silicon, and the like. In the casewhere a transition metal such as iron, copper, nickel, chrome, and thelike is contained in the alloy, an amount of the transition metal maypreferably be 100 wt ppm or less.

2) Negative Electrode

The negative electrode includes a current collector and a negativeelectrode layer formed on one or both of surfaces of the currentcollector and containing an active material, a conductive agent and abinder.

As the active material, the above-described active material forbatteries comprising the monoclinic β-type titanium composite oxidecontaining at least one element selected from the group consisting of V,Nb, Ta, Al, Ga, and In may be used. The at least one element iscontained in an amount of 0.03 wt % or more and 3 wt % or less.

In the embodiment, the non-aqueous electrolyte battery in which thenegative electrode including the negative electrode layer comprising theactive material is incorporated is capable of improving highcharacteristics and charge-discharge cycle property.

The conductive agent enhances a power collecting property of the activematerial and suppresses contact resistance with the current collector.Examples of the conductive agent include acetylene black, carbon black,and black lead.

The binder is capable of binding the active material with the conductiveagent. Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), a fluorine-based rubber, and a styrenebutadiene rubber.

The active material, the conductive agent, and the binder in thenegative electrode layer may preferably be contained at ratios of 70 wt% or more and 96 wt % or less, 2 wt % or more and 28 wt % or less, and 2wt % or more and 28 wt % or less. When the amount of the conductiveagent is less than 2 wt %, the power collecting property of the negativeelectrode layer is deteriorated to raise a risk of deterioration of highcurrent characteristics of the non-aqueous electrolyte battery. Further,when the amount of the binder is less than 2 wt %, a binding propertybetween the negative electrode layer and the current collector aredeteriorated to raise a risk of deterioration of the cycle property. Onthe other hand, it is preferable to keep each of the amounts of theconductive agent and the binder to 28 wt % or less in order to attainhigh capacity.

The current collector may preferably be an aluminum foil or an aluminumalloy foil containing an element such as Mg, Ti, Zn, Mn, Fe, Cu, and Si.The aluminum foil and the aluminum alloy foil are electrochemicallystable within a potential range which is nobler than 1.0 V vs Li/Li⁺.

The negative electrode is produced by preparing a slurry by suspendingthe active material, the conductive agent, and the binder into ageneral-purpose solvent, coating the slurry on the current collector,drying, and pressing, for example. Alternatively, the negative electrodemay be prepared by forming the active material, conductive agent andbinder into pellets to form a negative electrode layer, and forming thenegative electrode layer on the current collector.

3) Positive Electrode

The positive electrode includes a current collector, and a positiveelectrode layer(s) formed on one surface or both surfaces of the currentcollector and comprising an active material, a conductive agent and abinder.

As the active material, an oxide, a polymer, or the like may be used,for example.

As the oxide, manganese dioxide (MnO₂), iron oxide, copper oxide, andnickel oxide, in each of which lithium is occluded as well as lithiummanganese composite oxide (e.g., Li_(x)Mn₂O₄ and Li_(x)MnO₂), lithiumnickel composite oxide (e.g., Li_(x)NiO₂), lithium cobalt compositeoxide (Li_(x)CoO₂), lithium nickel cobalt composite oxide (e.g.,LiNi_(1-y)CO_(y)O₂), lithium manganese cobalt composite oxide (e.g.,Li_(x)Mn_(y)CO_(1-y)O₂), spinel type lithium manganese nickel compositeoxide (e.g., Li_(x)Mn_(2-y)Ni_(y)O₄), lithium phosphor oxide having anolipine structure (e.g., Li_(x)FePO₄, Li_(x)Fe_(1-y)Mn_(y)PO₄,Li_(x)CoPO₄), iron sulfate (Fe₂(SO₄)₃), and vanadium oxide (V₂O₅) areusable. Here, x and y may preferably be 0<x≦1 and 0≦y≦1.

As the polymer, a conductive polymer material such as polyaniline andpolypyrrole or a disulfide-based polymer material may be used. Sulfur(S) and carbon fluoride are also usable for the active material.

Examples of a preferred active material include lithium manganesecomposite oxide (Li_(x)Mn₂O₄), lithium nickel composite oxide(Li_(x)NiO₂), lithium cobalt composite oxide (Li_(x)CoO₂), lithiumnickel cobalt composite oxide (LiNi_(1-y)CoyO₂), spinel type lithiummanganese nickel composite oxide (Li_(x)Mn_(2-y)Ni_(y)O₄), lithiummanganese cobalt composite oxide (Li_(x)Mn_(y)CO_(1-y)O₂), and lithiumiron phosphate (Li_(x)FePO₄), each of which has a high positiveelectrode voltage. Here, x and y may preferably be 0<x≦1 and 0<y≦1.

A more preferred active material is lithium cobalt composite oxide orlithium manganese composite oxide. Since these active materials havehigh ion conduction property, diffusion of lithium ions in the positiveelectrode active material hardly progresses to a rate-controlling stepin the combination with the above-described negative electrode activematerial. Therefore, the active materials are excellent in compatibilitywith the lithium titanium composite oxide in the negative electrodeactive material.

The conductive agent enhances a power collecting property of the activematerial and suppresses contact resistance with the current collector.Examples of the conductive agent include a carbonaceous substance suchas acetylene black, carbon black, and black lead.

The binder is capable of binding the active material with the conductiveagent. Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), and a fluorine-based rubber.

The active material, the conductive agent, and the binder in thepositive electrode layer may preferably be contained at ratios of 80 wt% or more and 95 wt % or less, 3 wt % or more and 18 wt % or less, and 2wt % or more and 17 wt % or less. The conductive agent exhibits theabove-described effect when the amount thereof is 3 wt % or more. Theconductive agent suppresses decomposition of the non-aqueous electrolyteon surfaces of the conductive agent under high temperature storage whenthe amount thereof is 18 wt % or less. The binder enables to attainsatisfactory positive electrode strength when the amount thereof is 2 wt% or more. The binder reduces the content of a binder which is aninsulating material in the positive electrode and reduces internalresistance when the amount thereof is 17 wt % or less.

The current collector may preferably be an aluminum foil or an aluminumalloy foil containing an element such as Mg, Ti, Zn, Mn, Fe, Cu, and Si.

The positive electrode is produced by preparing a slurry by suspendingthe active material, the conductive agent, and the binder into ageneral-purpose solvent, coating the slurry on the current collector,drying, and pressing, for example. Alternatively, the positive electrodemay be prepared by forming the active material, conductive agent andbinder into pellets to form a positive electrode layer, and forming thenegative electrode layer on the current collector.

4) Non-Aqueous Electrolyte

Examples of the non-aqueous electrolyte include a liquid non-aqueouselectrolyte which is prepared by dissolving an electrolyte, for example,into an organic solvent and a gel non-aqueous electrolyte which is acomposite of a liquid electrolyte and a polymer material.

The liquid non-aqueous electrolyte may preferably be obtained bydissolving an electrolyte into the organic acid at a concentration of0.5 M or more and 2.5 M or less.

Examples of the electrolyte include lithium salts of lithium perchlorate(LiClO₄), lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate(LiBF₄), lithium hexafluoro arsenate (LiAsF₆), lithiumtrifluoromethasulfonate (LiCF₃SO₃), and bistrifluoromethylsulfonylimitritium [LiN(CF₃SO₂)₂] and mixtures thereof. The electrolyte maypreferably be hardly-oxidized even in high potential, and LiPF₆ is mostpreferred.

Examples of the organic solvent include a cyclic carbonate such aspropylene carbonate (PC), ethylene carbonate (EC), and vinylenecarbonate; a chain carbonate such as diethyl carbonate (DEC), dimethylcarbonate (DMC), and methylethyl carbonate (MEC); a cyclic ether such astetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolan(DOX); a chain ether such as dimethoxyethane (DME) and diethoxy ethane(DEE); γ-butyrolactone (GBL); acetonitrile (AN); and sulfolane (SL). Theorganic solvents may be used alone or in the form of a mixture solvent.

Examples of the polymer material include polyvinylidene fluoride (PVdF),polyacrylonitrile (PAN), and polyethylene oxide (PEO).

The organic solvent may preferably be the mixture solvent obtained bymixing at least two organic solvents selected from the group consistingof propylene carbonate (PC), ethylene carbonate (EC), and (diethylcarbonate [DEC]) or the mixture solvent containing γ-butyrolactone(GBL).

5) Separator

Examples of the separator include a porous film containing polyethylene,polypropylene, batteryulose, or polyvinylidene fluoride (PVdF) and anonwoven fabric of a synthetic resin. The porous film may preferably bemade from polyethylene or polypropylene, which improves safety due toits capability of being molten at a certain temperature and of blockinga current.

Hereinafter, a non-aqueous electrolyte battery according to theembodiment (e.g., a flat non-aqueous electrolyte battery in which theouter case is made from a laminated film) will be described in moredetails with reference to FIG. 1 and FIG. 2. FIG. 1 is a sectional viewshowing a thin non-aqueous electrolyte battery, and FIG. 2 is anenlarged view of a part A of FIG. 1. Further, the diagrams are not morethan those which are schematically drawn for the purpose of illustrationand understanding of the invention. Shapes, dimensions, ratios, and thelike in the diagrams may partially be different from actual devices, anddesigns thereof can be appropriately be changed by taking the followingdescription and well-known technologies into consideration.

A flat, spiral electrode group 1 is housed in a sac-like outer case 2made from a laminated film which is obtained by inserting an aluminumfoil into two resin layers. The flat, spiral electrode group 1 is formedby spirally winding a laminate obtained by laminating a negativeelectrode 3, a separator 4, a positive electrode 5, and a separator 4 inthis order from the outermost member and press-molding. The negativeelectrode 3 which serves as an outermost shell has a structure that anegative electrode layer 3 b is formed on an inner surface of a negativeelectrode current collector 3 a as shown in FIG. 2. The rest of thenegative electrodes 3 have a structure that the negative electrode layer3 b is formed on both surfaces of the current collector 3 a. An activematerial in the negative electrode layer 3 b comprises monoclinic β-typetitanium composite oxide containing at least one element selected fromthe group consisting of V, Nb, Ta, Al, Ga, and In, the at least oneelement being contained in an amount of 0.03 wt % or more and 3 wt % orless. The positive electrode 5 has a structure that a positive electrodelayer 3 b is formed on both surfaces of a current collector 5 a.

In the vicinity of an outer periphery of the flat, spiral electrodegroup 1, a negative electrode terminal 6 is connected to the negativeelectrode current collector 3 a of the negative electrode 3 serving asthe outermost shell, and a positive electrode terminal 7 is connected tothe positive electrode current collector 5 a of the inner positiveelectrode 5. The negative electrode terminal 6 and the positiveelectrode terminal 7 are extended from an opening of the sac-like outercase 2 to the outside. For example, the liquid non-aqueous electrolyteis injected through the opening of the sac-like outer case 2. The flat,spiral electrode group 1 and the liquid non-aqueous electrolyte arecompletely sealed by heat-sealing the opening of the sac-like outer case2 with the negative electrode terminal 6 and the positive electrodeterminal 7 being inserted into the opening.

For the negative electrode terminal, a material which has electricalstability and conductivity when a potential is within a range of from1.0 to 3.0 V vs Li/Li⁺ may be used. Specific examples thereof includealuminum or an aluminum alloy containing an element such as Mg, Ti, Zn,Mn, Fe, Cu, and Si. The negative electrode terminal may preferably be amaterial which is the same as that used for the negative electrodecurrent collector in order to reduce a contact resistance with thenegative electrode current collector.

For the positive electrode terminal, a material which has electricalstability and conductivity when a potential is within a range of from3.0 to 4.25 V vs Li/Li⁺ may be used. Specific examples thereof includealuminum or an aluminum alloy containing an element such as Mg, Ti, Zn,Mn, Fe, Cu, and Si. The positive electrode terminal may preferably be amaterial which is the same as that used for the positive electrodecurrent collector in order to reduce a contact resistance with thepositive electrode current collector.

Hereinafter, a battery pack according to the embodiment will bedescribed in detail.

The battery pack according to the embodiment has a plurality of theabove-described non-aqueous electrolyte batteries (electric batteries),in which the electric batteries are connected and disposed in series, inparallel, or in series and in parallel.

The battery pack has an excellent cycle property.

More specifically, the above-described non-aqueous electrolyte batteryaccording to the embodiment includes the negative electrode containingthe monoclinic β-type titanium oxide containing at least one elementselected from the group consisting of V, Nb, Ta, Al, Ga, and In and iscapable of improving the high current characteristics and thecharge-discharge cycle property while exploiting the high capacity ofthe monoclinic β-type titanium oxide. As a result, the battery packobtained by incorporating a plurality of the batteries is capable ofimproving the charge-discharge cycle property.

Hereinafter, the battery pack according to the embodiment willspecifically be described with reference to FIG. 3 and FIG. 4. As thebattery, the flat non-aqueous electrolyte battery shown in FIG. 1 isused.

A plurality of batteries 21 form an assembled battery 23, in which thebatteries 21 are layered in such a manner that the negative electrodeterminal 6 and the positive electrode terminal 7 extended to the outsideare oriented to an identical direction and fastened by an adhesive tape22. The batteries 21 are connected in series as shown in FIG. 4.

A printed wiring board 24 is opposed to a lateral surface of theelectric battery 21 in which the negative electrode terminal 6 and thepositive electrode terminal 7 is extended. As shown in FIG. 4, athermistor 25, a protection circuit 26, and a communication terminal 27for communication with an external appliance are mounted on the printedwiring board 24. An insulating plate (not shown) is attached to asurface of the protection circuit board 24 which is opposed to theassembled battery 23 in order to avoid unnecessary connection withwirings of the assembled battery 23.

A positive electrode lead 28 is connected to the positive electrodeterminal 7 positioned at the lowermost layer of the assembled battery23, and a leading end thereof is inserted into a positive electrodeconnector 29 of the printed wiring board 24 for electric connection. Anegative electrode lead 30 is connected to the negative electrodeterminal 6 positioned at the uppermost layer of the assembled battery23, and a leading end thereof is inserted into a negative electrodeconnector 31 of the printed wiring board 24 for electric connection. Theconnectors 29, 31 are connected to the protection circuit 26 throughwirings 32, 33 formed on the printed wiring board 24.

The thermistor 25 is used for detecting a temperature of the electricbattery 21, and a detection signal thereof is sent to the protectioncircuit 26. The protection circuit 26 can block a plus wiring 34 a and aminus wiring 34 b between the protection circuit 26 and thecommunication terminal 27 for communication with external applianceunder a predetermined condition. The predetermined condition may be thedetection temperature of the thermistor 25 which is equal to or a higherthan a predetermined temperature, for example. Alternatively, thepredetermined condition may be a detection of excessive charge,excessive discharge, excessive current, or the like of the electricbattery 21. The detection of excessive charge is performed on each ofthe electric batteries 21 or all of the electric batteries 21. In thecase of performing the detection on each of the electric batteries 21, abattery voltage may be detected, or a positive potential or a negativepotential may be detected. In the latter case, a lithium electrode to beused as a reference electrode is inserted into each of the electricbatteries 21. In the case of FIG. 3 and FIG. 4, a wiring 35 for voltagedetection is connected to each of the electric batteries 21, and adetection signal is sent to the protection circuit 26 through the wiring35.

A protection sheet 36 made from a rubber or a resin is disposed on eachof three surfaces of the assembled battery 23 except for the lateralsurface from which the positive electrode terminal 7 and the negativeelectrode terminal 6 are projected.

The assembled battery 23 is housed in a housing container 37 togetherwith the protection sheets 36 and the printed wiring board 24. Morespecifically, the protection sheets 36 are disposed on inner surfaces ina longitudinal direction of the housing container 37 and an innersurface in a width direction, and the printed wiring board 24 isdisposed on an inner surface in the width direction at an opposite side.The assembled battery 23 is position in a space enclosed by theprotection sheets 36 and the printed wiring board 24. A cover 38 isattached to an upper surface of the housing container 37.

A heat-shrinkable tape may be used for fixing the assembled battery 23in place of the adhesive tape 22. In this case, the protection sheetsare disposed on both sides of the assembled battery, and theheat-shrinkable tape is put around the assembled battery 23, followed byheat shrinkage of the heat-shrinkable tape for bundling the electricbattery.

Though the example of series connection of the electric batteries 21 isshown in FIG. 3 and FIG. 4, parallel connection or connection in whichseries connection and parallel connection are combined may be employedin order to increase a battery capacity. It is possible to connect theassembled battery packs in series or in parallel.

Further, the aspect of the battery pack may appropriately be changeddepending on application. The application of the battery pack maypreferably include those applications in which the excellent cycleproperty is exhibited when a high current is drawn. Specific examplesinclude application as a power source of a digital camera andapplication to a vehicle such as a two- or four-wheeled hybrid electricvehicle, a two- or four-wheeled electric vehicle, and a power-assistedbicycle. The application to a vehicle is particularly suitable.

As described above, it is possible to obtain the non-aqueous electrolytebattery having the excellent high temperature property by using themixture solvent obtained by mixing at least two solvents selected fromthe group consisting of propylene carbonate (PC), ethylene carbonate(EC), and diethyl carbonate (DEC) or the non-aqueous electrolytecontaining γ-butyrolactone (GBL). The battery pack including a pluralityof the non-aqueous electrolyte batteries is particularly suitable foruse in vehicles.

Hereinafter, examples of the embodiment will be described. However, theembodiment is not limited to the examples described below insofar as theembodiment does not deviate from the scope of the present invention.

Example 1 Manufacture of Positive Electrode

To start with, a slurry was obtained by adding 90 wt % of a lithiumnickel composite oxide (LiNi_(0.82)Co_(0.15)Al_(0.03)O₂) powder, 5 wt %of acetylene black as a conductive agent, and 5 wt % of polyvinylidenefluoride (PVdF) to N-methylpyrrolidone (NMP) and mixing, and the slurrywas applied on both surfaces of a current collector made from analuminum foil having a thickness of 15 μm, followed by drying andpressing, thereby manufacturing a positive electrode having an electrodedensity of 3.15 g/cm³.

<Manufacture of Titanium Composite Oxide>

To start with, niobium oxide (Nb₂O₅), potassium carbonate (K₂CO₃), andanatase type titanium oxide (TiO₂) were mixed, followed by baking at1000° C. for 24 hours to obtained K₂Ti₄O₉ including Nb. The obtainedK₂Ti₄O₉ was subjected to particle size adjustment by dry pulverizationusing zirconia balls and then washed with pure water to obtain a protonexchange precursor. The obtained proton exchange precursor was throwninto a 1M hydrochloric acid solution, followed by stirring under anenvironment of 25° C. for 12 hours, thereby obtaining a proton exchangeproduct.

A titanium composite oxide was produced by baking the obtained protonexchange product in air at 350° C. for 3 hours.

An X-ray diffraction of the obtained titanium composite oxide wasconducted under the conditions described below. As a result, the X-raydiffraction pattern shown in FIG. 5 was obtained, and it was thusconfirmed that a main substance forming the titanium composite oxide ismonoclinic β-type titanium composite oxide belonging to JCPDS: 46-1237.

<Measurement Method>

A standard glass holder having a diameter of 25 mm was filled with asample, and a measurement was conducted by employing wide angle X-raydiffractometry. A measurement apparatus and conditions are describedbelow.

(1) X-ray diffraction apparatus: D8 ADVANCE (tube type) manufactured byBruker AXS.

X-ray source: CuKα radiation (using Ni filter)

Output: 40 kV, 40 mA

Slit system: Div. Slit; 0.3°

Detector: LynxEye (high speed detector)

(2) Scanning method: 2θ/θ continuous scanning

(3) Measurement range (20): 5 to 100°

(4) Step width (2θ): 0.01712°

(5) Counting time: 1 s/step

An Nb concentration of the obtained titanium composite oxide wasmeasured by employing ICP emission spectroscopy. As a result, it wasconfirmed that the Nb concentration was 0.11 wt %.

<Manufacture of Negative Electrode>

A slurry was prepared by adding 90 wt % of the obtained titaniumcomposite oxide powder, 5 wt % of a black lead powder having an averageparticle diameter of 3.4 μm, and 5 wt % of polyvinylidene fluoride(PVdF) to N-methylpyrrolidone (NMP) and mixing. The slurry was appliedon both surfaces of a current collector made from an aluminum foilhaving a thickness of 15 μm, followed by drying. After that, a negativeelectrode having an electrode density of 2.0 g/cm³ was manufactured bypressing.

<Manufacture of Electrode Group>

The positive electrode, a separator made from a porous film ofpolyethylene having a thickness of 25 μm, the negative electrode, andthe separator were laminated in this order and spirally wound, followedby heat-pressing at 90° C., thereby obtaining a flat, spiral electrodegroup having a width of 30 mm and a thickness of 1.8 mm. The obtainedelectrode group was housed in an outer case made from a laminated film,followed by vacuum drying at 80° C. for 24 hours. The laminated film hada structure that a polypropylene layer is formed on both surfaces of analuminum foil having a thickness of 40 μm, and a thickness of thelaminated film was 0.1 mm.

<Preparation of Liquid Non-Aqueous Electrolyte>

Ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed at avolumetric ratio of 1:2 to obtain a mixture solvent. LiPF₆ which was anelectrolyte was dissolved at a concentration of 1M into the mixturesolvent to prepare a liquid non-aqueous electrolyte.

<Production of Non-Aqueous Electrolyte Secondary Battery>

The liquid non-aqueous electrolyte battery was injected into the outercase housing the electrode group. After that, the outer case wascompletely sealed by heat-sealing to obtain a non-aqueous electrolytesecondary battery having the above-described structure shown in FIG. 1as well as a width of 35 mm, a thickness of 2 mm, and a height of 65 mm.

Examples 2 to 13, Comparative Examples 1 and 2

14 types of non-aqueous electrolyte secondary batteries were produced inthe same manner as in Example 1 except for using as the negativeelectrode active material titanium composite oxides each comprisingmonoclinic β-type titanium composite oxide containing at least oneelement selected from Nb, V, Ta, Al, Ga, and In, the at least oneelement being contained in an amount shown in Table 1.

A resistance of each of the obtained secondary batteries of Examples 1to 13 and Comparative Examples 1 and 2 was measured, and then acharge-discharge cycle test of repeating charge-discharge of 1Ccharge/1C discharge was conducted. The resistance measurement wasperformed at an alternating current impedance of 1 kHz.

The resistance of each of the secondary batteries is shown in Table 1 asa ratio to Comparative Example 1 that is a criterion. Further, a ratioof 100th discharge capacity to an initial discharge capacity, i.e., adischarge retention rate (%) is shown in Table 1. As the resistance, thealternating current impedance at 1 kHz was measured.

TABLE 1 Content Capacity Contained of element Resistance retentionelement [wt %] [ratio] rate [%] Example 1 Nb 0.11 0.88 96 Comparative —— 1.00 62 Example 1 Example 2 Nb 0.03 0.92 94 Example 3 Nb 0.32 0.85 96Example 4 Nb 1.01 0.85 95 Example 5 Nb 1.99 0.88 90 Example 6 Nb 2.980.90 88 Comparative Nb 5.01 1.20 25 Example 2 Example 7 V 0.11 0.90 92Example 8 Ta 0.12 0.90 91 Example 9 Al 0.11 0.91 93 Example 10 Ga 0.090.92 90 Example 11 In 0.09 0.92 88 Example 12 Nb/Ta 0.31/0.12 0.85 96Example 13 Nb/V 0.32/0.11 0.85 96

As is apparent from Table 1, the secondary batteries of Examples 1 to 13have smaller resistances as compared to Comparative Examples 1 and 2and, therefore, have the excellent charge-discharge cycle property.Particularly, the secondary batteries of Examples 1 to 6, 12, and 13, ineach of which the titanium composite oxide obtained by adding Nb to themonoclinic β-type titanium composite oxide is used as the negativeelectrode active material, have the more excellent charge-dischargeproperty.

Though the embodiment of the present invention is described in theforegoing, the present invention is not limited to the embodiment andcan be changed into various modes within the scope of the inventionrecited in claims. Further, it is possible to modify the presentinvention into various modes within the range which does not deviatefrom the scope of the invention at a practical stage. Further, it ispossible to form various inventions by appropriately combining theplurality of constituent elements disclosed in the embodiment.

1. An active martial for batteries comprising monoclinic β-type titaniumcomposite oxide containing at least one element selected from the groupconsisting of V, Nb, Ta, Al, Ga, and In, the at least one element beingcontained in an amount of 0.03 wt % or more and 3 wt % or less.
 2. Theactive material of claim 1, wherein the at least one element occupies aTi site of the titanium composite oxide.
 3. A non-aqueous electrolytebattery comprising: an outer case: a positive electrode housed in theouter case; a negative electrode housed in the outer case with beingspatially separated from the positive electrode and containing an activematerial; and a non-aqueous electrolyte contained in the outer case,wherein the active material comprises monoclinic β-type titaniumcomposite oxide containing at least one element selected from the groupconsisting of V, Nb, Ta, Al, Ga, and In, the at least one element beingcontained in an amount of 0.03 wt % or more and 3 wt % or less.
 4. Thebattery of claim 3, wherein the at least one element is Nb alone or amixture of Nb and V, Nb and Ta, or Nb, V, and Ta.
 5. The battery ofclaim 3, wherein the at least one element occupies a Ti site of themonoclinic β-type titanium composite oxide.
 6. The battery of claim 3,wherein the positive electrode comprises lithium nickel composite oxideor lithium manganese composite oxide.
 7. The battery of claim 3, whereinthe outer case is formed of a laminated film.
 8. The battery of claim 3,which is for in-vehicle use.
 9. A battery pack comprising a plurality ofthe non-aqueous electrolyte batteries defined in claim 3, in which thebatteries are connected to each other in series, in parallel, or inseries and in parallel.
 10. The battery pack of claim 9, furthercomprising a protection circuit capable of detecting a voltage of eachof the non-aqueous electrolyte batteries.